Field of the Invention
The present invention relates to a focus detection apparatus and method, method of controlling a focus detection apparatus and an image capturing apparatus and, more particularly, to focus detection processing in an image capturing apparatus such as a camera.
Description of the Related Art
Japanese Patent Laid-Open No. 58-24105 discloses, as a focus detection apparatus designed to detect the focus state of an imaging optical system, an apparatus designed to perform focus detection by a so-called pupil division method using a two-dimensional image sensor having a microlens formed on each pixel. In the focus detection apparatus disclosed in Japanese Patent Laid-Open No. 58-24105, the photoelectric conversion portion of each pixel constituting an image sensor is divided into a plurality of portions, and the divided photoelectric conversion portions receive light beams passing through different regions of the pupil of an imaging optical system through a microlens.
In addition, Japanese Patent Laid-Open No. 2005-106994 discloses an image capturing apparatus which performs focus detection by the pupil division method using a CMOS sensor as a type of image sensors. The image capturing apparatus disclosed in Japanese Patent Laid-Open No. 2005-106994 has a structure in which some pixels of many pixels constituting a CMOS sensor include photoelectric conversion portions each divided into two portions to detect the focus state of an imaging optical system. These two divided photoelectric conversion portions receive light beams passing through different regions of the pupil of the imaging lens through a microlens. It is possible to detect a focus state by detecting the phase difference between a pair of signals obtained from the divided photoelectric conversion portions. In addition, there is conventionally proposed a technique of adding a pair of signals obtained from a photoelectric conversion portion divided into two portions for each pixel and handling the resultant value as a pixel value from a general imaging pixel.
On the other hand, there is available a function of selecting an AF frame size and an AF frame position relative to a field angle in accordance with an imaging scene when setting an AF frame in a camera in accordance with user settings or, in some case, the result obtained by a main object detection system.
In the above technique of performing phase difference AF on an imaging plane, it has been considered how much pixel data for focus detection are to be read out and held. When, for example, holding signals from the entire sensor surface, the data amount from the sensor with each photoelectric conversion portion being divided into two portions is twice the data amount from the sensor whose photoelectric conversion portions are not divided. This will impose a heavy load on a processing system on the subsequent stage. With an increase in data amount, it is necessary to implement parallel processing or a high clock rate. In addition, a heat problem occurs, and it is necessary to take countermeasures against heat, resulting in difficulty in achieving low cost.